Contact means for electric circuit breakers

ABSTRACT

A contact arrangement for circuit breakers includes a movable contact plug and a stationary sheath contact. In the sheath contact, a plurality of contact fingers are arranged in ring formation and are pressed against the contact plug by means of leaf springs punched out of sheet material. Each leaf spring is loosely inserted in a longitudinal groove in the associated contact finger in such a way that the spring action occurs in the plane of the spring.

United States Patent Inventor Sven Bachler Ludvika. Sweden Appl. No.823,770 Filed May 12, 1969 Patented Feb. 2, 1971 Assignee AllmannaSvenska Elektriska Aktiebolaget Vasteras, Sweden a Swedish CorporationPriority May 15, 1968 Sweden 6525/68 CONTACT MEANS FOR ELECTRIC CIRCUITBREAKERS 8 Claims, 3 Drawing Figs.

US. Cl...-. 200/166, 200/ l 70 Int. Cl H0lh l/44, HOlh 1/50 [50] Fieldof Search ZOO/16681, 166133. 166B5, 16636, 16688, 166C, 166D, 166E,166H,146,150.5, 110

[56] References Cited UNITED STATES PATENTS 2,300,893 1 H1942 Hayford200/166(E) 2,891,] 34 6/1959 Ramrath 200/170 3,127,492 3/1964 Date..200/ l 66(B1 )UX Primary Examiner-H. 0. Jones Attorney-JenningsBailey, Jr.

ABSTRACT: A contact arrangement for circuit breakers includes a movablecontact plug and a stationary sheath contact. In the sheath contact, aplurality of contact fingers are arranged in ring formation and arepressed against the contact plug by means of leaf springs punched out ofsheet material. Each leaf spring is loosely inserted in a longitudinalgroove in the associated contact finger in such a way that the springaction occurs in the plane of the spring.

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JNVENTOR. 5V5 N BAC HLE'R CONTACT MEANS FOR ELECTRIC CIRCUIT BREAKERSBACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates to a contact means of the type comprising a contactplug anda sheath contact surrounding the contact plug, said sheathcontact consisting of a plurality of contact fingers extending in thedirection of said contact plug and being arranged in ring formationbetween the contact plug and a surrounding contact housing and arrangedto be pressed radially against the contact plug by means of leaf springsarranged between the contact housing and the contact fingers.

2. The Prior Art The main purpose of the invention is to effect acontact means of the above-mentioned type in which the parts forming thesheath contact can be manufactured and assembled in such a way that thecontact means becomes less expensive than similar, previously knownarrangements. It is also desirable for the contact means to be rathercompact, particularly if it is to be used in oil-minimum circuitbreakers for indoor use. With such circuit breakers the question ofspace is extremely important and it is also from the safety point ofview desirable that the quantity of oil required is as small aspossible. With this type of circuit breaker the contact means is oftenarranged so that, to a considerable extent, it determines the outerdimensions of the circuit breaker.

With a sheath contact of the type mentioned above, it is most usual touse helical springs in order to effect the contact pressure. To be ableto fix such springs in the contact the contact fingers or thesurrounding contact housing must be provided with recesses, guidingpegs, guide sheaths or the like. The contact fingers or the housing musttherefore be pressed or cast in a special shape or be otherwisemachined, which considerable increases the cost of the contact. Helicalsprings are also rather space-consuming.

By using leaf springs instead of helical springs it has been possible toreduce the space required by the contact means considerable. Inpreviously known construction, leaf springs have been used which operateperpendicularly to their surface. The springs have usually beenpositioned by riveting or screwing them to the contact housing orcontact fingers which must be provided with special holes for thispurpose, possibly threaded. This considerably complicates themanufacture. Furthermore the clamping usually causes unfavorablestressing of the springs.

SUMMARY OF THE INVENTION The contact means according to the invention isof the type of sheath contact means using leaf springs so that the spacerequired is considerably less than with sheath contacts having helicalsprings. The invention is characterized in that the contact fingers andpossibly also the contact housing are manufactured from rod material,which is produced, for example, by

means of extrusion, having the final cross section of the fingers or thehousing, respectively, longitudinal grooves being arranged in thecontact fingers and/or in the surrounding contact housing, said grooveshaving the same cross section along the entire length of the contactfingers or housing, respectively, said leaf springs being looselyinserted in said grooves. This construction simplifies the manufactureof the contact means considerably, since the contact fingers can beproduced directly by cutting them from the rod material, usually copper,and need no further machining apart from possible silver-plating orother surface treatment. Since the springs are held in position only bytheir positioning in the grooves in the contact fingers or contacthousing, assembly of the sheath contact is considerably simplified andthe strain on the springs is more uniformly distributed over the lengthof the spring, thus decreasing the risk of a spring breaking.

A particularly advantageous further development of the invention ischaracterized in that each spring is shaped and arranged in such a waythat the spring action occurs in the plane of the spring. Since thesprings are punched out of, for example, steel sheeting and given such acontour that they can yield edgewise, the space requirement will only bethe thickness of the spring times the resilience. The space necessaryfor the spring is thus considerably less than for the conventional leafspring for which the space requirement, calculated in crosssectionalarea, will be the width of the spring times the resilience. The spacerequired can be further reduced by arranging the spring for the mostpart so that it is set in to the contact finger.

One end of the contact fingers is suitably gripped by an arcing ringsupported by the contact housing at the end situated nearest the contactisolating point and the other end of the contact fingers is pressedagainst a stationary, peg-shaped contact part in the sheath contact.Thus no special conducting connection for the passage of current betweenthe contact fingers and the stationary contact member is required andthe contact fingers can be arranged loosely in the contact. Thisconsiderably simplifies the construction.

The contact springs are suitably shaped so that their pressure point isplaced nearest the end of the fingers which is pressed against thestationary contact part of the sheath contact. In this way greaterspring action is obtained against the stationary contact part thanagainst the contact plug, which is desirable partly because the contactfingers are pivotably arranged around the stationary contact, which mustconsequently be shaped have a rounded surface in axial direction and thecontact surfaces are thus less than with a cylindrical contact plug, andpartly because the stationary contact part is not intended to be areplaceable component and arcing must therefore be completely avoided.

So that the best possible contact is obtained between, on the one side,the contact fingers and, on the other side, the contact plug and thestationary contact part of the sheath contact, respectively, it issuitable for the surface of the contact fingers facing the contact plugto be concave, suitably cylindrical, with the same radius of curvatureas the contact plug. So that the same type of contact finger may be usedtogether with contact plugs of different diameters the contact surfaceof the contact fingers may have several different radii of curvatuireincreasing in tangential direction from the symmetry axis of thesurface.

BRIEF DESCRIPTION OF THE DRAWING The invention will be further describedwith reference to an embodiment shown by way of example in theaccompanying drawings. FIG. I shows a central axial section through asheath contact according to the invention, FIG. 2 shows a cross sectionthrough the sheath contact along the line Il-Il in FIG. 1 and FIG. 3,finally, shows an end view of a contact finger of the sheath contact.

The contact means shown in FIGS. 1 and 2 comprises a movable contactplug 1 which cooperates with a stationary sheath contact 2. It is ofcourse also possible to arrange the contact plug stationary and thesheath contact movable. The end of the contact plug 1 consists of acontact shoe of coppertungsten, not shown. The sheath contact 2 consistsof a plurality of contact fingers 3 extending in the direction of thecontact plug 1 and placed in ring formation between the contact plug 1and a surrounding contact housing 4. The contact fingers 3 are pressedradially against the contact plug I with the help of leaf springs 5,which are punched out of steel sheeting (spring steel) about 1 mm. thickand are provided with a longitudinal hole 6 and otherwise shaped to giveeffective spring action in the plane of the material. The springs 5 arepartly set in in narrow radial grooves in the contact fingers 3. Thecontact fingers 3 are made from copper rods. At the front end eachfinger is provided with a shoe 8 of copper-tungsten. Otherwise thesection is unbroken along the entire length of the finger. At the bottomof the sheath contact is a pegshaped stationary contact part 9. Thecurrent transfer between the base of the contact finger 3 and thestationary contact part 9 takes place in the same manner as the transferto the plug 1. One and the same spring 5 is utilized to maintain thecontact pressure at both current-transfer points. During connection anddisconnection of the contact means the contact finger 3 performs arolling movement towards the stationary contact part 9, which iselliptically rounded in axial direction. The contact surfaces at thecurrent-transfer point against the contact part 9 are thereforerelatively small and for this reason a greater spring force is requiredagainst the stationary part 9 than against the plug 1, as mentionedabove. This is efiected by positioning the pressure point 10 of thespring nearer to the stationary part 9.

The front end of the contact housing 4 supports an arcing ring 11 ofcopper-tungsten. This ring 11 is shaped so that an annular groove 12 isformed into which the front end of the contact fingers projects. In thisway both the contact fingers 3 and the springs 5 are held in position inthe contact without the need for screw joints or other retainingelements.

in order to obtain high current loading capacity there should be goodcontact between the contact finger 3 and the contact plug 1 or contactpart 9, respectively. From this point of view the inwardly facingsurface of the contact finger should preferably have the same radius ofcurvature as the contact plug 1. However, it is usually desirable to beable to use one and the same contact finger section with contact plugsof different diameters. This can be achieved when manufacturing thecontact fingers by using a copper section shaped as shown in FIG. 3. Inthe area A, the contact finger thushas a radius of curvature of, forexample, 8 mm. in the areas B a radius of 11.5 mm. and in the areas C aradius of 12.5 mm. This contact finger can thus be used for threedifferent plug diameters, namely 16,23 and 25 mm.

The contact means shown as an example is particularly simple tomanufacture and assemble which is due in the first place to the contactfingers being given such a shape that they can be made, for example,from extruded rods, so that the retaining of the contact springs canalso be arranged in the simplest manner. Due to the special shape andplacing of the springs the contact means also needs extremely littlespace.

However, the invention is not limited to the embodiment shown. Severalmodifications are feasible within the scope of the following claims. Forexample, instead of using leaf springs arranged to yield on edge, it isalso possible to use normal leaf springs which operate perpendicularlyto their surface.

I claim:

1. A contact means for electric circuit breakers comprising a contacthousing, a contact plug and a sheath contact. said sheath contactsurrounding said contact plug and comprising a plurality of contactfingers, said contact fingers extending in the direction of said contactplug and arranged in ring formation between said contact plug and thecontact housing, leaf springs pressing said contact fingers radiallyagainst said contact plug, said springs punched out of sheet materialand arranged between said contact housing and said contact fingers. saidcontact fingers having longitudinal grooves therein, said grooves havingthe same cross section along the entire length of the contact fingers,said springs loosely inserted in said grooves.

2. A contact means according to claim 1, in which each spring exerts aforce in the plane of the spring.

3. A contact means according to claim 1, in which each spring issubstantially housed in the associated contact finger.

4 A contact means according to claim 1, in which said contact housing isprovided at one end with an arcing ring, which is arranged to engage oneend of the contact fingers.

5. A contact means according to claim I, in which a pegshaped stationarycontact part is arranged centrally at the bottom of the contact housing,the base end of said contact fingers pressed against said stationarycontact part.

6. A contact means according to claim 5, in which one and the samespring effects contact pressure both against said contact plug andagainst said stationary contact part, the pressure point of the springbeing situated nearer said stationary contact part.

7. A contact means according to claim 1, m which the sur-

1. A contact means for electric circuit breakers comprising a contacthousing, a contact plug and a sheath contact, said sheath contactsurrounding said contact plug and comprising a plurality of contactfingers, said contact fingers extending in the direction of said contactplug and arranged in ring formation between said contact plug and thecontact housing, leaf springs pressing said contact fingers radiallyagainst said contact plug, said springs punched out of sheet materialand arranged between said contact housing and said contact fingers, saidcontact fingers having longitudinal grooves therein, said grooves havingthe same cross section along the entire length of the contact fingers,said springs loosely inserted in said grooves.
 2. A contact meansaccording to claim 1, in which each spring exerts a force in the planeof the spring.
 3. A contact means according to claim 1, in which eachspring is substantially housed in the associated contact finger. 4 Acontact means according to claim 1, in which said contact housing isprovided at one end with an arcing ring, which is arranged to engage oneend of the contact fingers.
 5. A contact means according to claim 1, inwhich a peg-shaped stationary contact part is arranged centrally at thebottom of the contact housing, the base end of said contact fingerspressed against said stationary contact part.
 6. A contact meansaccording to claim 5, in which one and the same spring effects contactpressure both against said contact plug and against said stationarycontact part, the pressure point of the spring being situated nearersaid stationary contact part.
 7. A contact means according to claim 1,in which the surface of said contact fingers facing said contact plughas a concave surface to fit the contact plug.
 8. A contact meansaccording to claim 7, in which the surface of said contact fingersfacing said contact plug has several different radii of curvature.